Spinal instability is often attributed to undesirable excessive motion between vertebrae and can cause significant pain and morbidity. The instability may result from a number of causes, including abnormalities of the vertebrae, the intervertebral discs, the facet joints, and connective tissue around the spine. These abnormalities may arise from diseases, disorders or defects of the spine from trauma or bone degradation, such as osteoarthritis, or degenerative disc disease. When the spine becomes unstable, the vertebral column becomes misaligned and may produce micromotion between adjacent vertebrae. Vertebral misalignment and micromotion may result in wear to the vertebral bone surfaces and ultimately generate severe pain. These conditions are often chronic and create progressive problems for the sufferer.
Known treatments for spinal instability can include long-term medical management or surgery. Medical management is generally directed at controlling the symptoms, such as pain reduction, rather than correcting the underlying problem. For some patients, this may require chronic use of pain medications, which may alter the patient's mental state or cause other negative side effects. Surgical treatment typically includes decompression procedures to restore normal disc height, realign the column, and alleviate the pain.
Recently, a variety of interspinous vertebral devices have become available. These devices are typically implanted between the spinous processes of two or more adjacent vertebrae. By stabilizing the spinous processes in this way, significant stress may be taken off the intervertebral discs to prevent disease progression or to improve conditions such as spinal stenosis. In addition, vertebral motion may be controlled without severely altering the anatomy of the spine.
These devices can be secured between adjacent spinous processes using a number of different mechanisms. For example, such devices can include sharp barbs or other surface projections that engage the bony surface of a spinous process. In addition, flexible ligaments or sutures can be placed around the implants and adjacent bone. In some cases, the devices may be rigidly attached to the spinous process using a bone screw or other suitable bone anchor to prevent the interspinous device from migrating or slipping out of position. When the device is fastened to the spinous process in this manner, the device allows for rigid, fusion promoting securement.
It is desirable to therefore provide a device that can fit interspinously and, more desirably, interlaminarly, between adjacent vertebrae to enhance the stability of the spine at that segment. It is further desirable to provide such devices with features that cooperate with a bone graft, or bone substitute, component to facilitate fusion for even stronger stabilization.